1. Field of the Invention
This invention relates to improvements in a pressure relief valve adapted to release a part of the oil discharged from an oil pump of an internal combustion engine or the like.
2. Description of the Prior Art
A variety of pressure relief valves have been proposed and put into practical use for the purpose of releasing a part of oil discharged from an oil pump or the like. One of them is disclosed in Japanese Utility Model Provisional Publication No. 63-19088, in which the pressure relief valve includes a valve body or spool valve element which is slidably movable within a valve accommodating bore in accordance with balance established between the oil pressure of an oil pump and the biasing force of a spring, so as to accomplish an opening-and-closing control for first and second pressure relief holes or ports opened to the valve accommodating bore. The cross-sectional opening area of the first pressure relief hole is larger than that of the second pressure relief hole.
With such a pressure relief valve, the pressure relief holes are opened upon movement of the valve body in the valve accommodating bore thereby to allow excessive oil to be released through the pressure relief holes. At this time, as the oil pressure of the oil pump is increasing so as to move (displace) the valve body, first the first pressure relief hole having the larger cross-sectional opening area is opened. Then, the second pressure relief hole having the smaller cross-sectional area is opened in a process wherein the first relief hole is effectively increased in cross-sectional opening area.
Thus, in the above conventional pressure relief valve, the cross-sectional opening area of the first pressure relief hole is larger than that of the late opened second pressure relief hole. Besides, the second pressure relief hole is opened in the process of the first pressure relief hole increasing in cross-sectional opening area. As a result, an oil pressure characteristics C3 as indicated by a solid line in FIG. 10 is obtained under the action of the thus arranged pressure relief valve. In this oil pressure characteristics, at a point a in FIG. 10, the first pressure relief hole is opened so as to slightly reduce an increasing rate of oil pressure. At a point b in the process, the first pressure relief hole is effectively increased in cross-sectional opening area as the second pressure relief hole is opened to further reduce the increasing rate of oil pressure, so that the oil pressure is regulated to a generally constant level.
However, the thus obtained oil pressure characteristics indicated by the solid line in FIG. 10 is considerably higher than the required or ideal oil pressure characteristics indicated by a dotted line R in FIG. 10. As a result, pressure corresponding to an oblique-lined part between the solid and dotted lines causes excessive energy to be used in driving the oil pump.
It is an object of the present invention to provide an improved pressure relief valve which can effectively overcome drawbacks encountered in conventional pressure relief valves.
Another object of the present invention is to provide an improved pressure relief valve which can readily provide an oil pressure characteristics of a mechanism which requires pressurized oil, generally corresponding to a required oil pressure characteristics.
A further object of the present invention is to provide an improved pressure relief valve for an pump of an automotive internal combustion engine, which can readily provide an oil pressure characteristics of the pump, generally corresponding to a required oil pressure characteristics for the engine.
An aspect of the present invention resides in a pressure relief valve comprising a wall defining thereinside a valve accommodating bore. The wall is formed with a plurality of pressure relief holes through which oil in the valve accommodating bore is releasable to an outside of the wail. A valve body is provided to be slidably movable in the valve accommodating bore and along the wall under balance between oil pressure acting on the valve body in a first direction and biasing force of a spring acting on the valve body in a second direction opposite to the first direction. In this arrangement, after at least one of the pressure relief holes is opened to have a maximum cross-sectional opening area, remaining pressure relief holes are successively opened in a process of movement of the valve body in the first direction along an axis of the valve accommodating bore.
Another aspect of the present invention resides in a pressure relief valve comprising a wall defining thereinside a valve accommodating bore. The wall is formed with a plurality of pressure relief holes including first and second pressure relief holes through which oil in the valve accommodating bore is releasable to an outside of the valve accommodating bore. A valve body is provided to be slidably movable in the valve accommodating bore and along the wall under balance between oil pressure acting on the valve body in a first direction and biasing force of a spring acting on the valve body in a second direction opposite to the first direction. In this arrangement, the second pressure relief hole is opened after the first pressure relief hole is opened to have a maximum cross-sectional opening area in a process of movement of the valve body in the first direction along the axis of the valve accommodating bore.
A further aspect of the present invention resides in a pressure relief valve comprising a wall defining thereinside a valve accommodating bore. The wall is formed a slit-shaped pressure relief hole through which oil in the valve accommodating bore is releasable to an outside of the valve accommodating bore. The pressure relief hole is formed elongate in a direction along an axis of the valve accommodating bore. A valve body is provided to be slidably movable in the valve accommodating bore and along the wall under balance between oil pressure acting on the valve body in a first direction and biasing force of a spring acting on the valve body in a second direction opposite to the first direction. In this arrangement, the pressure relief hole is shaped such that its cross-sectional opening area linearly changes in a process of movement of the valve body in the first direction along the axis of the valve accommodating bore.
A further aspect of the present invention resides in a pressure relief valve for a pump driven by an internal combustion engine. The pressure relief valve comprises a wall defining thereinside a valve accommodating bore. The wall is formed with a plurality of pressure relief holes through which oil in the valve accommodating bore is releasable to an outside of the valve accommodating bore. A valve body is provided to be slidably movable in the valve accommodating bore and along the wall under balance between oil pressure acting on the valve body in a first direction and biasing force of a spring acting on the valve body in a second direction opposite to the first direction. In this arrangement, after at least one of the pressure relief holes is opened to have a maximum cross-sectional opening area in a low and medium engine speed operating range of the engine, remaining pressure relief holes are successively opened in a process of movement of the valve body in the first direction along the axis of the valve accommodating bore.
Accordingly, the pressure relief valve of the present invention can readily provide an oil pressure characteristics similar and generally corresponding to a required or ideal oil pressure characteristics for a mechanism requiring pressurized oil, for example, an internal combustion engine. As a result, the engine and an oil pump can be prevented from being forced to make excessive work.